Symbolism is prevalent throughout Fringe.
The white tulip is symbol of forgiveness and hope. Walter longs for a white tulip, which he believes will be a sign from God that he has forgiven Walter for breaking the universe. Walter believes that if he can forgive Walter for his actions, then so too can Peter. Walter receives a letter from Alistair Peck containing a white tulip. Peter and Olivia first meet as children in a field filled with white tulips. When Olivia regains her memories in the Alternate Timeline, but is rejected by Peter, a wilted white tulip can be seen on the table of the restaurant she meets Nina at for breakfast. At the end of the series, Peter receives a letter from Walter containing a white tulip, as Peck did for him.
The dandelion symbolizes the persistence of the human spirit. It is seen growing from "scorched earth" after the Observer invasion. It also is tied to Henrietta, who was seen playing with a dandelion in 2015 in the park.